molecules
Review

Nutritional Composition, Efficacy, and Processing of Vigna
angularis (Adzuki Bean) for the Human Diet: An Overview
Yao Wang 1,2 , Xinmiao Yao 1,2, * , Huifang Shen 1,2 , Rui Zhao 1,2 , Zhebin Li 1,2 , Xinting Shen 1,2 , Fei Wang 1,2 ,Kaixin Chen 1,2 , Ye Zhou 1,2 , Bo Li 1,2 , Xianzhe Zheng 3 and Shuwen Lu 1,2
1
2
3

*

Citation: Wang, Y.; Yao, X.; Shen, H.;
Zhao, R.; Li, Z.; Shen, X.; Wang, F.;
Chen, K.; Zhou, Y.; Li, B.; et al.
Nutritional Composition, Efficacy,
and Processing of Vigna angularis(Adzuki Bean) for the Human Diet:

Food Processing Research Institute, Heilongjiang Academy of Agricultural Sciences, Harbin 150086, China
Heilongjiang Province Key Laboratory of Food Processing, Harbin 150086, China
China School of Engineering, Northeast Agricultural University, Harbin 150030, China
Correspondence: cocoyococo@163.com; Tel.: +086-0451-86610259

Abstract: Adzuki beans are grown in several countries around the world and are widely popularin Asia, where they are often prepared in various food forms. Adzuki beans are rich in starch,and their proteins contain a balanced variety of amino acids with high lysine content, making
up for the lack of protein content of cereals in the daily diet. Therefore, the research on adzukibeans and the development of their products have broad prospects for development. The starch,
protein, fat, polysaccharide, and polyphenol contents and compositions of adzuki beans vary greatly
among different varieties. The processing characteristic components of adzuki beans, such as starch,isolated protein, and heated flavor, are reported with a view to further promote the processing anddevelopment of adzuki bean foods. In addition to favorable edibility, the human health benefitsof adzuki beans include antioxidant, antibacterial, and anti-inflammatory properties. Furtherly,
adzuki beans and extracts have positive effects on the prevention and treatment of diseases, including
diabetes, diabetes-induced kidney disease or kidney damage, obesity, and high-fat-induced cognitive
decline. This also makes a case for the dual use of adzuki beans for food and medicine and contributes
to the promotion of adzuki beans as a healthy, edible legume.
Keywords: adzuki bean; polysaccharides; polyphenols; health benefit

An Overview. Molecules 2022, 27,6079. https://doi.org/10.3390/
molecules27186079

1. Introduction
Academic Editors: Hongzhi Liu andAimin Shi
Received: 5 August 2022
Accepted: 13 September 2022
Published: 17 September 2022
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with regard to jurisdictional claims inpublished maps and institutional affiliations.

Copyright: © 2022 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms andconditions of the Creative Commons
Attribution (CC BY) license (https://Legumes are considered a beneficial part of traditional plant-based diets aroundthe world and are recommended in dietary guidelines from several organizations dueto their nutritional status and wide range of potential health benefits [1]. Vigna angularis(Willd.) Ohwi et Ohashi is a kind of traditional legume food, also known as red beans or
adzuki beans, which is native to China (Figure 1). Adzuki beans are grown all over theworld, including Africa, Europe, and the Americas, with Asia having the largest area of
adzuki beans. There are about 24 countries in the world planting adzuki beans; in addition
to China with the largest production area, Japan, North Korea, South Korea, Australia,
Thailand, India, Myanmar, the United States, Canada, Brazil, Colombia, New Zealand,
Zaire, Angola, and the former Soviet Union in the Far East all have a certain production
area [2]. At present, both the cultivation area and the total production of adzuki beans in
China are in first place in the world, and they are also exported to Japan, Malaysia, Korea,
the Philippines, and other countries [3]. Adzuki beans belong taxonomically to Vigna Saviin the Leguminosae family and are annual herbs that are frequently used as both medicine
and food because of their nutritional value and the presence of active substances [4,5]. It
is a self-pollinated, diploid plant, and the genome was mapped in 2015, which is of great
importance for molecular breeding, as well as genetic studies of adzuki beans [6].

creativecommons.org/licenses/by/4.0/).

Molecules 2022, 27, 6079. https://doi.org/10.3390/molecules27186079

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Molecules 2022, 27, x FOR PEER REVIEW

Molecules 2022, 27, 6079

2 of 15

is a self-pollinated, diploid plant, and the genome was mapped in 2015, which
2 ofis14of great
importance for molecular breeding, as well as genetic studies of adzuki beans [6].

FigureAdzukibean.
bean.(a)(a)Seedlings
Seedlingsof adzuki
beans(Vignaangularis)
the[7].
field[7]. (b)ofSeeds ofFigure 1.
1. Adzukiof adzuki
beans(Vignaangularis)in the infield(b) Seeds
adzuki(Vignaangularis).
angularis).
adzuki beans
beans (Vigna

Adzuki beans
receptivity
duedueto their
elegant
flavorflavor
and enjoyabletaste, taste,
Adzukibeanshave
havehighhigh
receptivity
to their
elegant
and enjoyable
with
rich
nutritionandrichnessinstarchandprotein.
Asafeasiblesourceofcarbohydrates,with rich nutrition and richness in starch and protein. As a feasible source of carbohythe starch of adzuki beans contains a large amount of resistant starch, which does not pose
drates,the starch of adzuki beans contains a large amount of resistant starch, which doesa significant burden on blood glucose after a meal [8–10]. Adzuki beans also contain a lot of
not pose a significant burden on blood glucose after a meal [8–10]. Adzuki beans also
dietary fiber and rich trace elements for body health, such as iron, calcium, and phosphorus;
containa lotofofphosphorus,
dietary fiberand rich trace
for body
such
as iron,the contents
manganese,
sulfur,elements
cobalt, cuprum,
andhealth,nickel in
the seedcoatscalcium,andphosphorus;
contentsof phosphorus,
manganese,
sulfur,cobalt,cuprum, andof adzuki
beans arethe
higherthan thoseof mung beans
and black beans[5,11].
For Asians,
nickelthe areseedcoatsingredientof adzuki
beans
arehigherinthan
thoseofoffoods
mung
beans
adzukiinbeans
a greatthatcan beprepareda variety(e.g.,
pasteandin black
pastries,
desserts,
porridge,
adzukirice,
adzukimilk, and ice
cream)
for preparedat least
beans[5,11].
For cake,
Asians,adzukibeans
arejelly,
a greatingredientthat
can bein aonebillionpeople
[12].
Over
the
years,
theproducts
ofadzuki
beans
have
been
developed,
variety of foods (e.g., paste in pastries, desserts, cake, porridge, adzuki rice, jelly, adzuki
mixingbean
withforcerealflour tomakebread,
pastry,andOvernutritious
food forpeople,milk,
andiceflourcream)
at leastonebillionpeople[12].
the years,
theproducts of
as
well
as
extracting
isolated
protein,starch,
and
fiber
for
applications
in
baby
food,
soft bread,adzuki beans have been developed, mixing bean flour with cereal flour to makedrinks, pudding macaroni; adding high amounts of dietary fiber into baked goods by using
pastry, and nutritious food for people, as well as extracting isolated protein, starch, andbean-coat flour; applying new extraction techniques to extract bioactive ingredients, such as
fiber
forphospholipids,
applications in
baby
food,
drinks,beanpudding
macaroni;amountscholine,andso on;and soft
developing
conveniencefoods,adding
such as highcannedofdietary
fiber
into
baked
goods
by
using
bean-coatflour;
applying
newextractionbeans, candied beans, and edible bean sprouts [13]. Balanced dietary structure plays an techniques
to roleextract
bioactivepeoples’
ingredients,
such ascholine,phospholipids,
and soimportantin improving
health levels.
Therefore,
researchon adzuki beansandon; andthe development
related products
help suchto improvedietarybeans,
nutritionand balance
dietarydeveloping
beanofconveniencefoods,
as canned
candiedbeans,and edible
structure.
Althoughseveral speciesof theVigna sp.plays
have been
described invariousreviews peobean
sprouts[13]. Balanced
dietary
structure
an importantrole
in improving
inrecentyears[14–28],few
reviews
have
been
conducted
foradzukibeans(TableS1
fromples’ health levels. Therefore, research on adzuki beans and the developmentof related
Supplementary
Materials).
Therefore,
we
want
to
provideacomprehensive
evaluationofproducts help to improve dietary nutrition and balance dietary structure. Althoughsevthe nutritional composition, processing characteristics, and human health benefits in ordereral species of the Vigna sp. have been described in various reviews in recent years [14–to provide some assistance in the research and development of adzuki beans.

28], few reviews have been conducted for adzuki beans (Table S1 from Supplementary
Materials).
Therefore,
we want to provide a comprehensive evaluation of the nutritional
2. Nutritional
Composition
2.1. Starchcomposition,
processing characteristics, and human health benefits in order to provide
someMicroscopic
assistance inthe researchand developmentof adzuki
observations
displaythat adzuki bean
starch beans.
is round or oval, withfew fissures on the surface, a complete outer edge, a granule diameter length greaterits width,Composition
an obvious polarized cross, an umbilical point located in the center of
2.thanNutritional

the starch granule, and the existence of a whorl structure similar to the annual rings oftrees. The starch of adzuki beans has a low pasting temperature, high paste viscosity, poor
observations
that adzuki bean
is roundor oval,with few
cold Microscopic
and heat stability,and easydisplay
aging characteristics[29]. starch
The starch
particle
sizes offissuresonthesurface,acomplete
outer
edge,
a
granulediameterlengthgreaterdifferent varieties of adzuki beans are between about 34.39~43.29 µm [30,31], even as highthan its
as 57.91~83.32µm [32].
These differences
due to thevarietiesof adzuki
or starch
width,
an obvious
polarized
cross, anare
umbilical
point
locatedin thebeans
centerof the starch
extraction
methods.
granule, and the existence of a whorl structure similar to the annual rings of trees. The
are some
differencesin total
starchcontent among
azuki
bean
varieties.poor
It wasstarchThereof adzuki
beans
has a low
pasting
temperature,
high
paste
viscosity,
cold andfound that, in early studies, the starch contents of 10 Chinese adzuki bean varieties ranged
heat stability, and easy aging characteristics [29]. The starch particle sizes of different vafrom 28.50% to 42.09%, and the amylopectin contents were 24.37% to 37.30% of the totalrietiesof adzuki beans are between about 34.39~43.29 μm [30,31], even as high as
seed [32]. Later studies showed that the total starch content of azuki beans could range
57.91~83.32[32]. These
differences
are dueto the[8].
varieties
adzukior starchfrom 44.55%μm
to 53.92%,
including
11.08~26.19%
amyloseIn 2019,ofthestarch beans
contents
extraction
methods.
of six adzuki bean species determined by Feng et al. ranged from 53.92% to 60.69%, with

2.1. Starch

There are some differences in total starch content among azuki bean varieties. It was
found that, in early studies, the starch contents of 10 Chinese adzuki bean varieties ranged

Molecules 2022, 27, 6079

3 of 14amylopectin accounting for 66.94% to 70.14% of the total starch content [30]. Another study
also determined that the amylose content was 28.30~35.43% of the total starch content inadzuki beans [9]. The total starch content of adzuki beans can reach from 28.50% to 60.69%,
among which the amylose and amylopectin contents vary greatly, with the amylose content
from 11.08–75.63% and amylopectin content from 24.37% to 88.92%. These differences may
arise from the varieties of adzuki beans, origins, years, and periods of seed collection of
adzuki beans.
2.2. Protein
The average protein level of azuki beans is 16.33~29.2%, which is 2–3 times higher
than those of cereal grains. The amino acid composition of azuki bean protein is in abalanced level, and they all meet the Food and Agriculture Organization of the United
Nations (FAO)/World Health Organization (WHO) label [33,34]. The protein contents of
10 Chinese adzuki bean varieties measured in a 2011 study ranged from 18.34 g/100 g to23.81 g/100 g [32]. A protein content analysis of 17 Chinese adzuki bean varieties revealed
that the protein mass fractions of azuki beans ranged from 22.83% to 25.41% [8]. An aminoacid analysis for different varieties of azuki beans revealed that all the varieties contained
eight essential amino acids for humans, with high levels of lysine, leucine, phenylalanine,and valine, with lysine as high as 1.98~1.82 g/100 g. These amino acids are deficient incereal protein, which reflects the unique nutritional value of the beans [35].
In a detailed study of adzuki bean protein, it was found that about 50% of the protein
was globulin, with the highest as 7S globulin, followed by 11S globulin. A circular dichroic
analysis showed that the protein was rich in α -helix and β -angle [36,37], where the thermal
polymerization caused the formation of disulfide bonds. The improvement of its nutritiveand digestibility undergoing heating treatment depended on the composition of aminoacids and thermal aggregation in the globulin [38].
2.3. Fat
The fat content in adzuki beans is at a low level, but there was a distinct difference inthe fatty acid contents of adzuki bean varieties, some at 0.4~1.3 mg/g in adzuki beans [9]or 0.34~0.72 mg/g [31], as well as at 0.48–0.56 mg/g in 2021 [39]. The total fat contents ofadzuki beans can range from 0.34 to 1.3 mg/g. There is also experimental confirmationof fatty acid content at about 5.45~6.31 mg/g, of which the dominant fatty acid, palmitic
acid, was 24.03~29.41%, linoleic acid content was 30.11~36.12%, and linolenic acid was
23.52~27.76%. These fatty acids accounted for 87.4% of the total fat. In addition, the fatty
acid content of stearic acid was 5.46~9.40%, and the oleic acid content was 4.51~7.01% [8].
These differences in the results of studies on fat content determination mainly may be due
to differences in adzuki bean varieties.
2.4. Polysaccharides
Legumes are rich in protein, fiber, various micronutrients, and polysaccharides [40].
The main active components of legumes are polysaccharides, which have antioxidant andimmunomodulatory activities [41–43]. Polysaccharides, as long-chain macromolecularcompounds, consist of more than 20 monosaccharides condensed by glycosidic bonds,
which can be broken down into monosaccharides and oligosaccharides by the action of
enzymes or acids [44]. The biological activity of polysaccharides depends mainly on thecomposition of the sugar, its molecular weight, and the type of glycosidic bond [41]. In
2015, water-extractable and alkali-extractable polysaccharides were obtained from theseeds of adzuki beans. The water-extractable polysaccharides were composed of rhamnose,arabinose, mannose, galactose, and glucose. The alkali-extractable polysaccharides werecomposed of rhamnose, arabinose, mannose, galactose, and galacturonic acid [42]. In recent
research, it was found that the polysaccharides in azuki beans were mainly composedof three fractions, with molecular weights of 131 kDa, 83 kDa, and 5 kDa, respectively.
Arabinose, galactose, glucose, xylose, mannose, and galacturonic acid in the polysaccha-

Molecules 2022, 27, 6079

4 of 14rides of azuki beans were found to be present in a ratio of 2.79:0.83:10.78:1.99:11.23:2.78,
respectively [45]. Adzuki bean polysaccharides have great potential for biological activity,
but there is not much research on them, and they are expected to have more research efforts.
2.5. Polyphenols
The study of polyphenols has been popular in bioactive substances of legumes inrecent years. More than 8000 polyphenols have been identified in different plant species,
where natural polyphenols mainly include phenolic acids, flavonoids, and tannins [46].
Phenolic substances in plants can be classified as soluble phenols and bound phenols,
depending on if they are extracted directly or not by organic solvents. In addition to
freeform, soluble phenolic extracts can also be bound in the form of ester, ether, andglycosidic bonds [47].
The content of polyphenols in adzuki beans may reach up to 3.73 mg/g, which ishigher than those in both mung beans and soybeans [48], even reaching 10.38 mg/g, with1.75 mg/g of free-state polyphenols and 8.63 mg/g of bound-state polyphenols. The content
of bound phenols is about five times higher than the content of free phenols [49]. In Gan’s
research, the total phenolic content extracted from adzuki beans was 13.37 mg/g [50]. In
Sreerama’s study, the total phenolic content in adzuki beans (black) was 8.78 mg/g, and thetotal phenolic content in adzuki beans (red) was 4.89 mg/g [51]. The total phenolic contentsof 17 Chinese adzuki bean varieties were 2.11~2.75 mg/g [8]. Table 1 shows different
amounts of monomeric phenols, with 22 from Amarowicz, 6 from Yan, and 11 from Li,
which determined the contents of monomeric phenols [52–55]. The differences in thepolyphenol contents of adzuki beans may be due to the varieties and origins.
Table 1. Phenolic compounds and their contents in adzuki beans.
Location of Extraction

Name of Compound

Adzuki Bean

Protocatechuic acid [52,55]

Adzuki Bean

Protocatechuic aldehyde [55]Adzuki Bean/Adzuki Bean Coattrans-p-Coumaric acid [52,55,56]

Adzuki Bean
Adzuki Bean
Adzuki Bean
Adzuki Bean
Adzuki Beantrans-p-Coumaroyl malic acid [55]
Epicatechin [55]
Epigallocatechin gallate [55]
Epicatechin glucoside [55]Catechin glucoside [55]Adzuki Bean/Adzuki Bean Coat

Quercetin [52,54–57]

Adzuki Bean
Adzuki Bean
Adzuki Bean
Adzuki Bean
Adzuki Bean
Adzuki Bean
Adzuki Bean
Adzuki Bean
Adzuki Bean
Adzuki Bean
Adzuki Bean
Adzuki Bean
Adzuki Bean
Adzuki Bean

Quercetin rutinoside [55]
Quercetin galactoside [55]
Quercetin glucoside [55]
Quercetin arabinoglucoside [55]Dihydroquercetin [55]Dihydroquercetin hexose [55]Dihydroquercetin derivative [55]Myricetin rhamnoside [55]
Kaempferol rutinoside [55]Tetrahydroxydihydrochalcone
glycoside [55]Procyanidin gallate [55]Procyanidin dimer [55]Procyanidin trimer [55]
Kaempferol-3-O-β-D-glucoside [53]Isoquercitrin [53]Adzuki Bean/Adzuki Bean Coat

Rutin [50,52–54,56,57]

Adzuki Bean

Isovitexin-600 -O-α-L-glucoside [53]Adzuki Bean/Adzuki Bean Coat

Chlorogenic acid [52,53,56,57]

Adzuki Bean

Analytical Method
UPLC-QTOF-MS and HPLC-QQQ-MS [52],HPLC-PAD [55]HPLC-PAD [55]UPLC-QTOF-MS and HPLC-QQQ-MS [52],HPLC-PAD [55], HPLC [56]HPLC-PAD [55]HPLC and LC/MS [54], HPLC-PAD [55]HPLC-PAD [55]HPLC-PAD [55]HPLC-PAD [55]UPLC-QTOF-MS and HPLC-QQQ-MS [52],HPLC and LC/MS [54], HPLC-PAD [55],HPLC [56,57]
HPLC-PAD [55]HPLC-PAD [55]HPLC-PAD [55]HPLC-PAD [55]HPLC-PAD [55]HPLC-PAD [55]HPLC-PAD [55]HPLC-PAD [55]HPLC-PAD [55]Content (µg/g)67.6 ± 4.01 [55], 13.94 ± 0.22 [52]7.71 ± 0.62 [55]31.3 ± 1.96 [55], 7.16 ± 0.06 [52]4.57 ± 0.69 [55]25.7 ± 2.06 [55]0.14 ± 0.02 [55]159.0 ± 8.31 [55]688.0 ± 35.6 [55]36.2 ± 1.54 [55], 3.07 ± 0.05 [52]38.2 ± 1.52 [55]46.9 ± 5.87 [55]181.0 ± 9.14 [55]42.8 ± 4.23 [55]1.15 ± 0.07 [55]
0.54 ± 0.02 [55]
1.35 ± 0.06 [55]212.0 ± 9.85 [55]38.2 ± 1.52 [55]HPLC-PAD [55]

0.55 ± 0.08 [55]HPLC-PAD [55]HPLC-PAD [55]HPLC-PAD [55]HPLC-ESI-TOF-MS [53]HPLC-ESI-TOF-MS [53]UPLC-QTOF-MS and HPLC-QQQ-MS [52],HPLC-ESI-TOF-MS [53], HPLC and
LC/MS [54], HPLC-PAD [55], HPLC
[56,57]
HPLC-ESI-TOF-MS [53]UPLC-QTOF-MS and HPLC-QQQ-MS [52],HPLC-ESI-TOF-MS [53], HPLC-PAD [55],HPLC [56,57]

12.4 ± 1.06 [55]213.0 ± 13.2 [55]41.8 ± 1.11 [55]1.6 ± 0.1 [53]0.8 ± 0.03 [53]420 ± 0.02 [50],4.1 ± 0.2 [53], 327.40 ± 5.43 [52]1.3 ± 0.03 [53]14.0 ± 1.3 [53], 1.76 ± 0.05 [52]Molecules 2022, 27, 6079

5 of 14

Table 1. Cont.
Location of Extraction

Name of Compound

Analytical Method

Content (µg/g)

Adzuki Bean
Adzuki Bean Coat

Benzyl-O-β-D-glucopyranoside [53]Gallic acid [56,57]

0.4 ± 0.01 [53]—Adzuki Bean/Adzuki Bean Coat

Catechin [52,54,56,57]

Adzuki Bean Coat
Adzuki Bean Coat
Adzuki Bean Coat
Adzuki Bean Coat
Adzuki Bean Coat
Adzuki Bean Coat

Epicatechin [56,57]
Procyanidin B2 [56,57]
Ferulic acid [56,57]
Isovitexin [57]Vitexin [57]Isorhamnetin [57]Adzuki Bean/Adzuki Bean CoatHyperoside [52,56,57]

Adzuki Bean Coat
Adzuki Bean Coat
Adzuki Bean Coat
Adzuki Bean
Adzuki Bean
Adzuki Bean
Adzuki Bean
Black Adzuki Bean
Black Adzuki Bean
Black Adzuki Bean
Black Adzuki Bean
Black Adzuki Bean

Kaempferol [56,57]
Syringic acid [56]Caffeic acid [56]4-Hydroxybenzoic acid [52]Luteolin [52]Daidzein [52]Glycitein [52]Delphinidin-3,5-O-digalactoside [58]Delphinidin-3,5-O-diglucoside [58]Delphinidin-3-O-galactoside [58]Delphinidin-3-O-glucoside [58]Delphinidin-3-O-rutinoside [58]Delphinidin-3-O-(p-coumaroyl)
glucoside [58]
Cyanidin-3-O-glucoside [58]
Petunidin-3-O-galactoside [58]
Petunidin-3-O-glucoside [58]
Petunidin-3-O-(p-coumaroyl)
glucoside [58]HPLC-ESI-TOF-MS [53]HPLC [56,57],
UPLC-QTOF-MS and HPLC-QQQ-MS [52],HPLC and LC/MS [54], HPLC [56,57]
HPLC [56,57]
HPLC [56,57]
HPLC [56,57]
HPLC [57]
HPLC [57]
HPLC [57]UPLC-QTOF-MS and HPLC-QQQ-MS [52],HPLC [56,57]
HPLC [56,57]
HPLC [56]HPLC [56]UPLC-QTOF-MS and HPLC-QQQ-MS [52]UPLC-QTOF-MS and HPLC-QQQ-MS [52]UPLC-QTOF-MS and HPLC-QQQ-MS [52]UPLC-QTOF-MS and HPLC-QQQ-MS [52]NMR and UPLC-Q-Orbitrap-MS/MS [58]
NMR and UPLC-Q-Orbitrap-MS/MS [58]
NMR and UPLC-Q-Orbitrap-MS/MS [58]
NMR and UPLC-Q-Orbitrap-MS/MS [58]
NMR and UPLC-Q-Orbitrap-MS/MS [58]Black Adzuki Bean
Black Adzuki Bean
Black Adzuki Bean
Black Adzuki Bean
Black Adzuki Bean

210.70 ± 5.58 [52]
—
—
—
—
—
—
2.59 ± 0.05 [52]———0.52 ± 0.12 [52]0.16 ± 0.01 [52]3.11 ± 0.19 [52]0.09 ± 0.01 [52]
—
—
—
—
—

NMR and UPLC-Q-Orbitrap-MS/MS [58]—

NMR and UPLC-Q-Orbitrap-MS/MS [58]
NMR and UPLC-Q-Orbitrap-MS/MS [58]
NMR and UPLC-Q-Orbitrap-MS/MS [58]———

NMR and UPLC-Q-Orbitrap-MS/MS [58]—3. Processing Properties
Botanical starch has three main stereoscopic structure forms according to different XRD
spectra patterns. Experiments have confirmed that type A starch is easier to digest thantype B and C starches. Type A starch is common in cereal starch, type B starch is common
in tubers, and type C starch is common in legumes and rhizomes. Studies have shown thatazuki bean starch also belongs to C-type crystal structure starch [39,59]. Type A starch, withthe components of short, lateral amylopectin chains and closed branching points, presents
peaks at around 2θ angles of 15◦ , 17◦ , 18◦ , and 23◦ . Type B starch has long side amylopectin
chains and distant branching points with clear diffraction peaks of 17◦ , while type C starch
is a mixture of type A and type B, such that the special crystal structures consisting of type
A and type B crystals give type C starch specific crystal tunability [60,61]. Azuki beans
contain ideal, slow-digesting starch, and it is the semi-crystalline C-type structure of the
starch that determines its slow-digesting properties. In common processing such as cooking,baking, and autoclaving, the destruction of crystal structure is disrupted, making the starchmore digestible than unprocessed starch [62]. Significant correlations were also foundbetween the starch content of azuki beans and the degree of pasting, pasting characteristics,
hardness, and crystallinity [63]. Polysaccharides are another very important carbohydrate
in legumes. The composition and molecular weight of polysaccharides play an importantrole in exerting bioactive effects [41]. A study confirmed some differences in composition
between water-extracted and alkali-extracted polysaccharides from adzuki beans [42].
However, research on the processing and extraction of adzuki bean polysaccharides isvery limited, and there are still many unsolved problems, which is a new research andexploration direction for scholars.
Compared to soybean protein, the adzuki bean protein isolate has high solubility ata lower pH. Under the same pH, the emulsification and oil-holding properties of adzuki
bean protein remains basically the same as those of soybean protein isolate, but the water
absorption, emulsification stability, and foaming stability are worse than those of soybean
protein isolate. In addition, both adzuki bean and soybean proteins had fine gelation
properties [64]. A study by Shen et al. confirmed that the solubility values of adzuki bean
protein from five species reached the lowest values around pH 4.0. In addition, there

Molecules 2022, 27, 6079

6 of 14

was a correlation between the protein properties, including the surface hydrophobicity,
emulsification, emulsion stability, water absorption, and oil absorption, of adzuki bean
protein [65].
Yao et al. found that microwave baking and drum roasting influenced the generationof characteristic volatile compounds for adzuki beans, such as furan, pyrazine, ketone,
alcohols, aldehydes, esters, pyrroles, sulfocompounds, phenols, and pyridine. Moreover,drum-roasted baked beans showed a higher flavor than that of microwave-baked beans.
A critical temperature and low moisture content of 116.5 ◦ C at a moisture content of 5.6%
(w.b.) in microwave baking and 91.6 ◦ C at a moisture content of 6.1% (w.b.) in drumroasting resulted in a rapid increase in acrylamide content [66].
Although adzuki beans are commonly consumed in daily life, their processing properties are still less studied. More research should be carried out on the processing characteristics of adzuki beans to develop a variety of adzuki bean series products, and it is of greatsignificance to expand the consumption population of adzuki beans.
4. Healthy Benefits
Adzuki beans are also a traditional medicine that have been used as a diuretic andantidote, as well as to alleviate symptoms of dropsy and beriberi in China [3]. Therefore,
research on adzuki beans and extracts of adzuki beans have long fascinated scientists.
Phytochemicals are non-nutritive, vegetative secondary components, with significant
differences in biochemistry, source distribution, and physiological effects [67]. Their biological activities, such as antioxidant [68], anti-inflammatory [69], and antibacterial [70]properties, have also been described to provide important, meaningful benefits to humanhealth. In studies on adzuki beans, it has been found that they are rich in phytochemicals,with important meaning for human health.
4.1. Antioxidant Activity
Legumes are rich in polyphenols, flavonoids, and proanthocyanidins, which are
phytochemicals with natural antioxidants [71,72]. Already, a study in 2009 indicated thatextracts from 15 common edible legumes had significant antioxidant activity [73]. The
antioxidant properties of the total phenols and total flavonoids of five legumes, including
black beans, mung beans, red adzuki beans, soybeans, and cowpeas, were investigated,
and it was found that the scavenging abilities of 1,1-diphenyl-2-picrylhydrazyl free radicals(DPPH·), hydroxyl radicals (·OH) and superoxide radicals (O2 − ·) of the five legumes wererelatively high [73]. Cowpeas, adzuki beans, mung beans, and broad beans had the abilityof scavenging DPPH·, Ferric ion reducing antioxidant power (FRAP), 2,20 -azino-bis (3-ehtylbenzothiazoline-6-sulfonic acid) diammonium salt radical free radicals (ABTS+·), andO2 − · [49].
For the antioxidant properties of adzuki beans, polysaccharides had great scavenging
ability for O2 − · and ·OH, which could effectively block the synthesis of nitrosamines, aswell as having some scavenging ability for sodium nitrite [74]. Polyphenols extracted
from adzuki bean coats were also shown to have scavenging abilities for DPPH·, O2 − ·,ABTS+·, ·OH, and the scavenging abilities for ABTS+· and ·OH were higher than that ofvitamin C [50,57]. In addition to polyphenols and polysaccharides, condensed tannins
showed a powerful antioxidant capacity for scavenging ABTS+· and FRAP [75]. Studies
have confirmed the ability of components in adzuki beans to scavenge a variety of free
radicals, which has led to the confirmation of the antioxidant capacity of adzuki beans.
4.2. Antimicrobial and Anti-Inflammatory Activity
Foodborne pathogenic bacteria contamination is a potential threat factor affecting
food safety and triggering public health events. Common pathogenic bacteria include
Escherichia coli, Salmonella, Staphylococcus aureus, and Listeria monocytogenes, etc. Thesepathogenic bacteria have strong resistance to environmental factors, such as dryness, acid,

Molecules 2022, 27, 6079

7 of 14salt, and heat, resulting in their long-term survival during food production, processing,and storage [76].
It was shown in 2021 that the addition of adzuki bean coat polyphenol extract inhibited
Listeria ATCC19119 and Salmonella ATCC14028 with minimum inhibitory concentrations of
625 µg/mL and 2500 µg/mL, respectively. The addition of adzuki bean coat polyphenol
extracts had significant effects on the protein and nucleic acid contents, cell membranepotential, intracellular ATP content, extracellular alkaline phosphatase content, and morphological changes of the bacteria [56]. It was also demonstrated that the polyphenolic
extracts in adzuki bean coats had inhibitory effects on two Gram-positive bacteria (B. cereus
and S. aureus), but not on Gram-negative bacteria (E. coli and S. typhimurium) [50].
Inflammation is an over-reactive immune response of the body to infection or tissue
damage that is associated with various diseases, such as inflammatory bowel disease,cancer, type 2 diabetes mellitus (T2DM), and cardiovascular disease [77,78]. In 2017,
scientists confirmed the positive effects of black adzuki beans on colon inflammation triggered by high-fat-diet-induced obesity in mice. The black adzuki beans decreased theconcentrations of lipopolysaccharides and circulating proinflammatory cytokines (such as
tumor necrosis factor (TNF)- α, interleukin (IL)-1β, and IL-6) in mice [79]. Another study
confirmed that an active peptide (KQS-1) isolated from extruded adzuki bean protein,sequenced as KQSESHFVDAQPEQQQR, exerted significant anti-inflammatory effects inlipopolysaccharide-induced RAW 264.7 macrophages and significantly reduced the production of IL-1, IL-6, TNF-α, and MCP-1 [80]. The antibacterial properties of adzuki beansreaffirm the potential function of extract from adzuki beans as a natural food preservative,
and studies on the anti-inflammatory properties of adzuki beans also verify the medicinal
and food properties of adzuki beans.
4.3. Antidiabetic Activity
It has been shown that the carbohydrates contained in legumes have a slow postprandial glycemic change and, therefore, most legumes are low-glycemic-index (GI) foods
compared to starch-based food crops [81]. In a simulated in vitro digestion test of beans, it
was found that the starch hydrolysis rate of adzuki beans was 31.42% after 2 h of in vitro
digestion compared to 78% for rice, indicating a lower starch hydrolysis rate of adzukibeans compared to rice [82]. Therefore, adzuki beans have a great advantage in terms ofstarch digestive properties for an antidiabetic diet.
In 2005, scientists found that the hot water extract of adzuki beans had some inhibitory
effects on α-amylase and glucosidase, which had some potential in the prevention of type
II diabetes [83]. Research in 2012 also confirmed that adzuki beans had inhibitory effects
on α-glucosidase and pancreatic lipase activities [51]. For further analysis of adzuki bean
extract, researchers identified (+)-catechin 7-O-β-D-glucopyranoside (C7G), (+)-epicatechin
7-O-β-D-glucopyranoside (E7G), and (+)-catechin as the main bioactive components. These
substances have an inhibitory effect on both α-amylase and α-glucosidase, and this inhibitory effect did not disappear after high-temperature heating [84].
Numerous experiments in mice have also confirmed the antidiabetic function of adzukibeans. Dietary supplementation with black adzuki bean extract significantly improved thehyperglycemia and homeostasis model assessment of insulin resistance index (HOMA-IR)
in high-fat-diet-induced glucose-intolerant obese C57BL/6J mice [85]. Adzuki bean extract
could potentially improve glucose intolerance in rats by upregulating the phosphorylationof serine/threonine protein kinase (AKT) and adenosine monophosphate-activated protein
kinase (AMPK) in the livers of diabetic rats [86]. In addition, an oral administration of
adzuki bean polysaccharides to rats could significantly reduce weight loss, fasting blood
glucose (FBG), and the concentration of serum triglyceride (TG). In addition, it reversed
dyslipidemia caused by diabetes, as evidenced by a reduction in triglycerides (TG) andelevated high-density lipoprotein cholesterol (HDL-C). With the increase in the expressionof insulin receptor (INSR), insulin receptor substrate-1 (IRS-1), phosphoinositide 3-kinase(PI3K), protein kinase B (AKT), and glucose transporter-2 (GLUT-2) in type 2 diabetic rats,

Molecules 2022, 27, 6079

8 of 14

it indicated that adzuki bean polysaccharides regulated glucose metabolism by activating
the PI3K/AKT signaling pathway, thus achieving an antidiabetic effect [87].
4.4. Hypolipidemic Activity
In addition to the antioxidant properties and its antidiabetic function, the hot water
extract of adzuki beans was shown to inhibit lipid accumulation in 3T3-L1 adipocytes andto reduce body weight and adipose tissue weight [88]. Rats fed with adzuki bean paste
were also found to reduce visceral fat accumulation and lower serum lipid levels in theadzuki-bean-paste-fed group more than the control group [89]. A high-fat diet feedinggroup supplemented with 15% adzuki beans and a control group were set up with miceand fed for 12 weeks. It was found that adzuki bean supplementation significantly reduced
high-fat-diet-induced obesity, lipid accumulation, serum lipids, and lipopolysaccharide(LPS) levels, which mitigated liver function damage and hepatic steatosis [90].
When mice fed a high-cholesterol diet were given 0.5 mL of a solution of adzuki
polyphenols for two weeks, the atherosclerotic index of experimental mice was significantly
lower than that of the control group, indicating a significant inhibitory effect of adzuki
polyphenols on serum cholesterol [91]. An 8-week trial evaluated in human subjects
confirmed there was a significant increase in high-density liptein cholesterol concentrationsin the participants receiving adzuki bean extract compared to a placebo, and no adverse
effects were observed in the participants [92]. All of these studies have effectively confirmed
the efficacy of adzuki beans in helping to resist to high-fat-diet-induced fat accumulationand in hypolipidemic activity, with no adverse effects in a safe manner.
4.5. Multiple Functions for Healthy Benefits
Adzuki beans have obvious medicinal and food homology. Diabetic kidney diseaseis associated with oxidative stress and inflammation. Scientists suggested that adzuki
bean extract may weaken streptozotocin-induced diabetic kidney injury by inhibiting
oxidation [93]. Another study also confirmed the positive effects of adzuki beans on thekidneys. Two surgeries on rats to obtain an animal model of moderate chronic kidneydisease in the study of Baracho et al. revealed that the levels of glucose, triglycerides,
very-low-density lipoproteins (VLDL), uric acid, alanine aminotransferase, urea, and serum
creatinine were significantly reduced in mice in the adzuki-bean-treated group compared tothe control and drug-treated groups, indicating the effective improvement of renal function
parameters of adzuki bean [94].
Studies on the hot water extract of adzuki beans adsorbed onto DIAION HP-20 resin
adsorption columns confirmed the inhibitory effect on experimental lung metastasis andthe invasion of B16-BL6 melanoma cells, as well as the adhesion and migration of B16BL6 melanoma cells to extracellular matrix components, and the study indicated that
hot water extract of adzuki beans may have a strong antimetastatic ability [83]. A study
showed an inhibitory effect of red bean extract (RBE) on muscle atrophy in an immobilized
hindlimb muscle of C57BL/6J mice. Red bean extract increased the grip strength, exercise
endurance, muscle weight, and muscle fiber area, which could significantly decrease themRNA expression of proteolytic-related genes, such as muscle ring finger and muscle
atrophy F-box, by the preventing the translocation of Forkhead box 3 [95]. Adzuki bean
extract may reduce the elevation of blood pressure by regulating endothelial nitric oxide
synthase (eNOS) and inducible nitric oxide synthase (iNOS) protein expression in the aorta
and kidney [96]. High-fat-diet-induced obesity has been associated with cognitive andmemory dysfunction.
Studies have confirmed the contribution of adzuki beans to the treatment of obesityinduced cognitive decline. For high-fat-fed mice, adzuki bean extract could improve their
spatial and recognition abilities. An increase in the ratios of their exploration of a novel
object or new routes was also confirmed in a T-maze and novel object recognition tests [97].
A study on adzuki bean sprout fermented milk was also found to relieve anxiety and mild
depression due to its richness in γ-aminobutyric acid (GABA) [98].

Molecules 2022, 27, 6079

aorta and kidney [96]. High-fat-diet-induced obesity has been associated with cognitiveand memory dysfunction.
Studies have confirmed the contribution of adzuki beans to the treatment of obesityinduced cognitive decline. For high-fat-fed mice, adzuki bean extract could improve their
spatial and recognition abilities. An increase in the ratios of their exploration of a novel
14
object or new routes was also confirmed in a T-maze and novel object recognition9 of
tests[97]. A study on adzuki bean sprout fermented milk was also found to relieve anxiety andmild depression due to its richness in γ-aminobutyric acid (GABA) [98].
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main active components of legumes and have a variety of biological activities, including
antioxidant and immunomodulatory activities [41–43]. Adzuki beans and their extracts
have positive effects on the treatment of many diseases, which may also be because of theirpolysaccharide components. In addition, the polyphenols of adzuki beans also play a very
important role in many aspects, such as antioxidant and anti-inflammatory activity.
5. Conclusions and Future Perspective
As a traditional Asian food, there are many varieties of adzuki beans with differencesin starch, protein, and fat contents and compositions that are rich in polysaccharides
and polyphenols. Due to the starchy nature of the beans and the phytochemicals, theconsumption of adzuki beans has various health benefits, which display positive effects on
the treatment of diseases. This establishes the feasible edibility of adzuki beans and their
medicinal value.
The domestication and research on adzuki beans have been conducted for many years,
but there are still some problems in the process of research. Bioactive components suchas phenols and polysaccharides in adzuki beans have been confirmed to play an important role in human health, but there are no relevant standards for the extraction of thesesubstances, resulting in differences in the identification and contents of substances due todifferences in extraction methods in the research process. This also provides an obstacle forthe further study of adzuki bean bioactive substances. Adzuki bean extract has a positiveeffect on many diseases, but the components of adzuki bean extract are complex, and theidentification and study of effective monomer components are limited. In addition, studies
on the polyphenols and polysaccharides of adzuki beans are often conducted by in vitro
experiments through extracts. However, the utilization rate of polyphenols and polysaccha-

Molecules 2022, 27, 6079

10 of 14rides in adzuki beans after eating, as well as how to maximize the retention of the bioactive
substances of adzuki beans in processing, is still little-studied. The change in the structureof polysaccharides may lead to a change in their biological activity, and chemical, physical, and biological methods can cause the change in the structure of polysaccharides [99].
However, the changes in polysaccharides and phytochemicals during processing and thebioactivity of adzuki beans after processing need to be further studied. Edible legumes
have some potential for intestinal probiotics, but there are few studies related to adzukibeans. To date, less research has been performed on adzuki beans at the genetic level. In
future studies, it is expected that more research can participate in the study of adzuki beans,
and the processed food of adzuki beans can be enjoyed by more people.
Supplementary Materials: The following are available online at https://www.mdpi.com/article/
10.3390/molecules27186079/s1, Table S1: Reviews on Vigna sp. from 2017 to 2022. References [14–28]
are also cited in Supplementary Materials.
Author Contributions: Writing—original draft preparation, Y.W.; literature collection, H.S. and R.Z.;
Figure made by software, X.S. and F.W.; editing, X.Z. and Z.L.; project administration, K.C. and Y.Z.;
funding acquisition, X.Y., S.L. and B.L. All authors have read and agreed to the published version of
the manuscript.
Funding: This research was funded by [Research funding for scientific research institutes in Heilongjiang Province] grant number [CZKYF2021B001]; [Agricultural Science and Technology Innovation Project of Heilongjiang Academy of Agricultural Sciences] grant number [HNK2019CX19];[Science and Technology Research Project of Heilongjiang Academy of Agricultural Sciences] grant
number [2021YYYF040].
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Conflicts of Interest: The authors declare that they have no conflict of interest.

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